1. Field of the Invention
The present invention relates to a seat cushion for a vehicle seat unit that comprises a cushioning pad such as an urethane foam upholstered with a seat covering, and, more particularly, to a seat cushion for a vehicle seat unit in which a planer electrically conductive clement is disposed between a cushioning pad and a seat covering.
2. Description of Related Art
Typically, a seat cushion of a front seat unit or a rear seat unit for a vehicle comprises an elastic cushioning pad such as an urethane pad and a seat covering with which the elastic cushioning pad is upholstered. Some types of seat cushion are provided with a planar conductive clement such as comprised of a flexible but inelastic planar film with an electrically conductive element buried therein (that is hereafter referred to as a planar conductive film) that is disposed between the cushioning pad and the seat covering. In one example, the planar conductive film is used as a planar sensor device that detects an occupant sitting on the seat cushion or an occupant such as an infant or a small child secured in a child safety seat on the seat cushion.
Reference is made to FIGS. 10 through 15 showing prior art seat cushions with a planer conductive film embedded in a seat cushion between a cushioning pad and a seat covering for the purpose of providing a brief background that will enhance an understanding of the present invention.
Referring to FIG. 10 showing one of the prior art seat cushions for a vehicle seat unit, a seat cushion 80 comprises an elastic cushioning pad 81 preferably made of an urethane foam with its seating surface entirely upholstered with a seat covering (not shown). The seat cushion 80 is provided with a flexible but inelastic planar conductive film 82 embedded therein between the seat cushioning pad 81 and the seat covering. The elastic cushioning pad 81 has a plurality of U-shaped tuck-in grooves 83 (only one of which is shown) extending in both lengthwise and transverse directions. The seat covering is locally retained the tuck-in grooves 83 for preserving a designed appearance of the seat cushion 80, and strip sections of the planer conductive film 82 are laid in the tuck-in grooves 83 in a U- or V-shape. According to the seat cushion 80, when the seat cushion 80 repeatedly experiences an external impact load from above, while the cushioning pad 81 elastically contacts and recovers repeatedly, nevertheless, the planar conductive film 82 does not contract. In consequence, the nip sections of the planar conductive film 82 in the tuck-in grooves 83 are repeatedly loosened and stretched and led into breakage or damage as shown in FIG. 11. Such breakage or damage of the strip section of the planar conductive film 82 causes an electric disconnection of the electrically conductive element at the broken or damaged strip section laid in the tuck-in groove 83. The electric disconnection of the electrically conductive element is made more marked, if the tuck-in grooves 83 is made deeper for design requirements. Modified shapes of tuck-in groove 83 such as shown in FIGS. 12 through 15 are conceivably effective to eliminate an occurrence of breakage or damage of the strip section of the planar conductive film 82 in the tuck-in groove 83.
Referring to FIG. 12 showing a seat cushion 80 having one of the variations of tuck-in groove, a cushioning pad 81 has a tuck-in groove 83 locally provided with bridges 84 so that the tuck-in groove 83 is locally made shallow at locations where strip sections of a planar conductive film 82 traverse the tuck-in groove 83.
According to the seat cushion 80 having the cushioning pad 81 with the tuck-in grooves 83 locally made shallow, while the planar conductive film 82 is advantageously prevented from causing breakage or damage that is conductive to an electric disconnection of the electrically conductive element buried in the planer conductive film 82, nevertheless, the tuck-in groove 83 at the bridges 84 is made too shallow for the seat covering to provide a sufficient tuck-in depth for the seat covering. This tends toward an unattractive appearance of the seat cushion 80 and, in consequence, leads the seat unit into less marketability.
Referring to FIG. 13 showing a seat cushion 80 having another variation of tuck-in groove, a cushioning pad 81 has a tuck-in groove 83 locally provided a narrow inverted trapezoidal recesses 85 across the tuck-in grooves 83 at locations where strip sections of a planar conductive film 82 are laid in the tuck-in grooves 83. The inverted trapezoidal recess 85 comprises a flat bottom 85a at a level with the bottom of the tuck-in groove 83 and walls 85b slanting in opposite directions. After laying a strip section of the planer conductive film 82 in the inverted trapezoidal recess 85 in keeping with the walls 85a and 85b, triangular retaining pads 85c are forced into triangular spaces formed in the cushioning pad 81 by the inverted trapezoidal recess 85 at opposite sides of the tuck-in groove 83 so as thereby to prevent the strip section of the planer conductive film 82 from coming up. The triangular retaining pad 85 is preferably different in material from the cushioning pad 81.
According to the tuck-in groove 83 shown in FIG. 13, while the strip section of the planar conductive film 82 is prevented from coming up, and hence from being broken or damaged, by the triangular holding pads 85, nevertheless, the incorporation of the triangular retainer pads 85 leads to an increase in costs and manpower for manufacturing the seat cushion 80.
Referring to FIGS. 14 and 15 showing a seat cushion 80 having still another variation of tuck-in groove, a cushioning pad 81 has a tuck-in groove 83 and inverted trapezoidal grooves 86 across the tuck-in groove 83 at locations where strip sections of a planar conductive film 82 is laid in the tuck-in grooves 83. The inverted trapezoidal groove 86 at opposite sides has an open top end flanked with a pair of rounded retaining protrusions 87 at each of opposite sides of the tuck-in groove 83. Each rounded retaining protrusion 87 is formed as an integral portion of the cushioning pad 81. The strip section of the planar conductive film 82 is forced into the inverted trapezoidal groove 86 passing through the retaining protrusions 87 and laid in the tuck-in groove 83.
According to the tuck-in groove 83 shown in FIGS. 14 and 15, the strip section of the planar conductive film 82 is prevented from coming up and out of the tuck-in groove 83 by the retaining protrusions 87. While the tuck-in groove 83 thus constructed is advantageous in preventing the planar conductive film 82 from being damaged or broken, and hence an electric disconnection of the electrically conductive element, nevertheless, the tuck-in groove 83 inevitably reaches aggravation of setting easiness of the strip sections of the planar conductive film 82. That is, if the retaining protrusion 87 is made larger in order to prevent the strip section of the planar conductive film 82 from coming up and out of the tuck-in groove 83, it becomes an onerous task to tuck the strip section of the planar conductive film 82 in the tuck-in groove 83.
Another idea on eliminating an occurrence of breaking of an electrically conductive layer or film of a planar occupant sensor of a seat unit is disclosed in Japanese Unexamined Patent Publication No. 2000-318503. This planar occupant sensor has a protective sheet with an extension inserted between cushioning pad of a seatback and an adhesive layer so as to prevent the electrically conductive layer or film from breaking. However, the protection sheet is used only for protecting the electrically conductive layer or film. In addition, the electrically conductive layer or film is not laid in tuck-in grooves.